Accelerated progression ofHoxa-9^−/− thymocytes to SP cells in 10-day FTOCs. (A) FACS analysis of thymocytes harvested from 10-day FTOCs using antibodies against CD4, CD8, and αβ TCR. Most of theHoxa-9^−/− cells have progressed through the DP stage to become mature SP cells. (B) Absolute numbers of T-cell subsets in 10-day FTOCs. Based on analyses from 3 separate FTOC experiments (representing 4 mutant and 6 wild-type thymuses), the numbers of SP mature cells in the mutant and normal FTOCs are not significantly different, but the number of Hoxa-9^−/− DP is markedly reduced.